In compression moulding and injection moulding large demands are often made on tight dimensional tolerances of the finished products. In order to maintain these tight tolerances, it is necessary in many applications for the raw material to be inserted in the mould cavity under very high pressure. This pressure can be so great that the material in the mould walls, often steel, is subjected to a re-crystalisation, so that the steel is compacted and the size of the cavity increases. This change in the mould is small but may be of great importance, e.g. if the mould has a core for giving shape to a hole through the product. At one end the core is fastened in one mould half and extends from the cavity wall of this half to the cavity wall in the other half of the mould. The other end of the core engages against the opposing cavity wall, and the engagement surface there between is here called the "core print". During material compression and dimensional changes in the mould during injection moulding a gap occurs between the core and the wall at the core print. The material to be moulded can penetrate into this gap and thereby blank off the hole through the product. In the known art, this is counteracted by the core being made somewhat longer than the distance between the opposing cavity walls. When the mould halves are pressed against each other in the injection moulding process, the core is elastically deformed by compression in its longitudinal direction. The dimensional change in the mould occuring during injection is compensated by the ability of the core to expand elastically in its longitudinal direction and engage with its free end against the cavity wall. The mentioned gap is thus prevented at the core print. However, the stresses occurring in the core at its compression are so great that the material is rapidly fatigued and the core cracks. This results in production downtime and costs for replacing the spoiled core.
A mould for injection moulding a plastics frame on a glass pane is illustrated in the Swedish patent No. 8300391-3. The mould has two halves, the cavities of which form a cavity corresponding to the shape of the frame. The edge parts of the glass pane project into the cavity and each of the mould havles has a projecting edge part engaging against the pane. To prevent the plastics material from coming out into the gap between the edge parts of the mould halves and the glass pane during moulding it is proposed that strips of elastic material are clamped in the gap. This method is only usable for relatively low pressures in the mould, and the method is complicated to apply.